Abstract: Fermentation pit is a kind of solid bioreactors with unique feature for brewing liquor, especially for Luzhou-flavor, which has significant effects on the quality of produced liquor. There exists a close and complicated correlation between pit age (using time) and microbial community. Taking the characteristic component phospholipid fatty acid (PLFA) in microbial cell membrane as an index, this paper studied the characteristics of the microbial community structure in the pit mud, fermented grains, and yellow water of different age (5-year, 100-year, and 300-year) fermentation pits. The results showed that the total PLFA content was the highest in pit mud, followed by in fermented grains, and in yellow water. The composition of PLFA differed with pit age, and the total PLFA content in yellow water decreased with increasing pit age. In pit mud, straight chain saturated fatty acid had the highest content, occupying 50.7-73.3% of total PLFA and being the highest in 300-year pit. As for the microbial community structure, the PLFA content characterizing Gram-positive (G⁺) anaerobic bacteria was higher in pit mud, and that characterizing Gram-negative (G^-) anaerobic bacteria was higher in fermented grains and yellow water. The PLFA content characterizing G⁺ and G^- bacteria in the pit mud of 100-year pit was higher than that in the pit mud of other ages’ pits, while the PLFA content characterizing fungi was higher in the pit mud, fermented grains, and yellow water of 5-year pit, as compared with other ages’ pits.Principal component analysis showed that the main varied microbial populations in 5- and 100-year pits were G^- bacteria and fungi, and the main varied microbial population in 300-year pit was of bacteria. The indices frequency index, Simpson index, and Shannon index could be chosen for characterizing the diversity of microbial community in fermentation pits.

Key words: phospholipid fatty acid, fermentation pit, microbial community